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Exploration of augmentation strategies in multi-modal retrieval-augmented generation for the biomedical domain

Primož Kocbek, Azra Frkatović-Hodžić, Dora Lalić, Vivian Hui, Gordan Lauc, Gregor Štiglic

University of Maribor digital library (University of Maribor), 2026

Abstract

Multi-modal retrieval-augmented generation (MMRAG) promises grounded biomedical QA, but it is unclear when to (i) convert figures/tables into text versus (ii) use optical character recognition (OCR)-free visual retrieval that returns page images and leaves interpretation to the generator. We study this trade-off in glycobiology, a visually dense domain. We built a benchmark of 120 multiple-choice questions (MCQs) from 25 papers, stratified by retrieval difficulty (easy text, medium figures/tables, hard cross-evidence). We implemented four augmentations—None, Text RAG, Multi-modal conversion, and late-interaction visual retrieval (ColPali)—using Docling parsing and Qdrant indexing. We evaluated mid-size opensource and frontier proprietary models (e.g., Gemma-3-27BIT, GPT-4o family). Additional testing used the GPT-5 family and multiple visual retrievers (ColPali/ColQwen/ColFlor). Accuracy with Agresti–Coull 95% confidence intervals (CIs) was computed over 5 runs per configuration. With Gemma-3-27BIT, Text and Multi-modal augmentation outperformed OCR-free retrieval (0.722-0.740 vs. 0.510 average accuracy). With GPT-4o, Multi-modal achieved 0.808, with Text 0.782 and ColPali 0.745 close behind

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